Carbon nanotube composite material and method for manufacturing the same

ABSTRACT

A carbon nanotube composite material ( 10 ) includes a matrix material ( 12 ) having two opposite surfaces ( 102 ) and ( 104 ), a number of CNTs ( 14 ) each having two opposite end portions ( 112 ) and ( 114 ) embedded in the matrix material. The two opposite end portions of each CNT extend to and, potentially, out of the respective two opposite surfaces of the matrix material. A method for manufacturing the carbon nanotube composite material includes the steps of: providing a substrate and forming a carbon nanotube array in a selective pattern thereon; providing a pair of protective layers, a respective protective layer being attached on a corresponding portion of ends of CNTs; filling clearances existing among CNTs and between the two protective layers with a matrix material; and removing the protective layers from CNTs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to commonly-assigned, co-pendingapplications: entitled, “THERMAL INTERFACE MATERIAL AND METHOD FORMAKING THE SAME”, filed * * * (Atty. Docket No. US7491); “THERMALINTERFACE MATERIAL AND METHOD FOR MANUFACTURING SAME”, filed * * *(Atty. Docket No. US7258); and “THERMAL INTERFACE MATERIAL AND METHODFOR MAKING THE SAME”, filed * * * (Atty. Docket No. US7257). Thedisclosures of the above-identified applications are incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention relates to composite materials and manufacturingmethods thereof and, more particularly, to a carbon nanotube compositematerial and a manufacturing method thereof.

DESCRIPTION OF RELATED ART

CNTs (Carbon NanoTubes) are tube-shaped structures composed of graphite.CNTs have a high Young's modulus, high thermal conductivity, and highelectrical conductivity, among other properties. Due to these and theother properties, it has been suggested that CNTs can play an importantrole in fields such as microelectronics, material science, biology, andchemistry.

A kind of thermally conductive material that conducts heat by using CNTshas been developed. The thermally conductive material is formed byinjection molding and has numerous CNTs incorporated in a matrixmaterial. A first surface of the thermally conductive material engageswith an electronic device, and a second surface of the thermallyconductive material engages with a heat sink. The second surface has alarger area than the first one, so that heat can be uniformly spread outto the larger second surface. However, the thermally conductive materialformed by injection molding is relatively thick. This increases a bulkof the thermally conductive material and reduces its flexibility.Furthermore, CNTs are disposed in the matrix material randomly and aremultidirectional in orientation. This random disposition means that heattends to spread uniformly through the thermally conductive material,retaining much of the heat within the heat transfer material.Accordingly, the heat does not spread efficiently from the first surfaceengaged with the electronic device to the second surface engaged withthe heat sink.

Therefore, a thin carbon nanotube composite material, with controllednanotube orientation within one or more selective patterns and, thus,with good thermal/electrical conductivity, and a method formanufacturing such a material is desired.

SUMMARY OF THE INVENTION

A carbon nanotube composite material includes a matrix material havingtwo opposite surfaces, a number of CNTs each having two opposite endportions embedded in the matrix material. The two opposite end portionsof CNTs respectively extend out of the two opposite surfaces of thematrix material.

A method for manufacturing the carbon nanotube composite materialincludes the steps of: providing a substrate and forming a carbonnanotube array in a selective pattern thereon, each carbon nanotube(CNT) in the carbon nanotube array having respective first and secondend portions; forming a first protective layer on the respective firstend portion of the CNTs; forming a second protective layer on therespective second end portion of the CNTs; filling clearances among theCNTs between the first protective layer and the second protective layerwith a matrix material; and removing the first protective layer and thesecond protective layer from the carbon nanotube array.

Other advantages and novel features will become more apparent from thefollowing detailed description when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the carbon nanotube composite material can be betterunderstood with reference to the following drawings. The components inthe drawings are not necessarily to scale, the emphasis instead beingplaced upon clearly illustrating the principles of the present carbonnanotube composite material. Moreover, in the drawings, like referencenumerals designate corresponding parts throughout the several views.

FIG. 1 is a schematic, isometric view of a carbon nanotube compositematerial according to a preferred embodiment;

FIG. 2 is a schematic, side view of the carbon nanotube compositematerial of FIG. 1;

FIG. 3 is a top view of the carbon nanotube composite material, in whichseveral carbon nanotube array patterns are provided, according to apreferred embodiment;

FIG. 4 is a flow chart of a method for manufacturing the carbon nanotubecomposite material of FIG. 1;

FIG. 5 to FIG. 9 are schematic views illustrating the manufacturingsteps 1-5 in FIG. 4; and

FIG. 10 is a diagram showing an electrical property of the carbonnanotube composite material according to a preferred embodiment.

The exemplifications set out herein illustrate at least one preferredembodiment of the present carbon nanotube composite material and themethod for manufacturing the same, and such exemplifications are not tobe construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 and FIG. 2, a carbon nanotube composite material 10,according to a preferred embodiment, includes a matrix material 12 and acarbon nanotube array 14. The matrix material 12 has a first surface 102and a second surface 104 opposite to the first surface 102. The carbonnanotube array 14 is embedded in the matrix material 12, the CNTs of thecarbon nanotube array 14 being uniformly dispersed in a desired pattern.Each CNT of the carbon nanotube array 14 has a first end portion 112 anda second end portion 114 opposite to the first end portion 112. The twoopposite end portions 112 and 114 advantageously extend at least to thetwo opposite surfaces 102, 104, respectively, and, in order tofacilitate a connection with other components, are, furtheradvantageously, exposed. If not exposed, however, the end portions 112and 114 are beneficially offered protection by the surrounding matrixmaterial 12 but do have the drawback of not being able to be asintimately connected to adjoining components as may be possible ifexposed. The matrix material 12 is, advantageously, selected from thegroup consisting of silica gel, polyethylene glycol, polyester, epoxyresin, and acrylic.

The two opposite surfaces 102 and 104 are substantially parallel to eachother. The carbon nanotube array 14 is beneficially in a form of analigned carbon nanotube array. Each CNT of the carbon nanotube array 14is substantially parallel to one another and further substantiallyperpendicular to the two opposite surfaces 102 and 104. Thus, each CNTof the carbon nanotube array 14 can provide a direct, shortest-distancethermal conduction path and/or electrical transmission path from onesurface to another of the matrix material 12.

Referring to FIG. 3, a patterned carbon nanotube composite material 20includes a matrix material 22 having two opposite surfaces and a numberof patterned carbon nanotube arrays 24 embedded therein. Each CNT of thecarbon nanotube arrays 24 includes two opposite end portion thatrespectively extend from two opposite surfaces of the matrix material22. The carbon nanotube arrays 24 can be patterned in a desiredposition, e.g., of an Integrated Circuit (IC) chip and/or can be formedinto a geometrical figure, such as a circle, rectangle, ellipse, square,or any combination thereof. The carbon nanotube array 24 is sandwichedbetween the IC chip and a printed circuit board (PCB) for improvingelectrical connection therebetween and/or thermal conduction from the ICchip to ambient and/or a heat sink.

As shown in FIG. 4, a method for manufacturing the carbon nanotubecomposite material 10 is provided. The method employs an in-situinjection molding process, which comprises the steps of:

Step 1, providing a substrate and forming a patterned carbon nanotubearray thereon, each carbon nanotube having a first end portion and anopposite second end portion;

Step 2, forming a first protective layer on the first end portions ofthe CNTs;

Step 3, removing the substrate and forming a second protective layer onthe second end portion of the CNTs;

Step 4, filling clearances among the CNTs between the first protectivelayer and the second protective layer with a matrix material; and

Step 5, removing the protective layers from the CNTs.

Referring to FIGS. 5 through 9, the method for manufacturing the carbonnanotube composite material 10, in accordance with the preferredembodiment, is described below, in detail.

In step 1, as shown in FIG. 5, a substrate 16 is provided and apatterned carbon nanotube array 14 is formed thereon. Each CNT of thecarbon nanotube array 14 has a first end portion 112 and an oppositesecond end portion 114, and a number of clearances 116 are defined amongthe adjacent CNTs. The carbon nanotube array 14 can be formed, forexample, by a chemical vapor deposition method.

The chemical vapor deposition method for manufacturing the carbonnanotube array 14 generally includes steps of: firstly, forming acatalyst film (not labeled) on the substrate 16 and then growing carbonnanotube array 14 thereon by providing a carbon source gas at hightemperature. The substrate 16 is beneficially made from a materialselected from the group consisting of glass, silicon, metal, and metaloxide. The catalyst film can, usefully, be made from material selectedfrom the group consisting of iron (Fe), cobalt (Co), nickel (Ni), and analloy thereof. The carbon source gas can be, e.g., methane, ethylene,propylene, acetylene, methanol, ethanol, or some mixtures thereof. Inthe preferred embodiment, a silicon wafer is used as the substrate 16,iron as the catalyst film, and ethylene as the carbon source gas. Aniron film pattern having a thickness of about 5 nanometers (nm) isformed on the substrate 16 and is annealed in air at 300° C. Then, thesubstrate 16 with the iron film deposited thereon is placed into achemical vapor deposition chamber (not labeled), an ethylene gas isprovided therein at 700° C., and then the carbon nanotube array 14 isproduced. The carbon nanotube array 14 grown is about 0.3 millimeters(mm) high and substantially perpendicularly to the substrate 16.

In step 2, as shown in FIG. 6, a first protective layer 18 is formed onthe first end portions 112 of the carbon nanotube array 14. The firstprotective layer 18 includes a polyester film 124 and a pressuresensitive adhesive layer 122 thereon. In the preferred embodiment, thepressure sensitive adhesive layer 122 is about 0.05 mm thick and iscoated on a side of the polyester film 124. More specifically, the firstprotective layer 18 can be attached to the carbon nanotube array 14 asfollows: placing the first protective layer 18 on the carbon nanotubearray 14 with the pressure sensitive adhesive 122 facing towards thefirst end portions 112; pressing the first end portions 112 of thecarbon nanotube array 14 into the pressure sensitive adhesive layer 122,thereby directly attaching the first protecting layer 18 to the carbonnanotube array 14. The pressure sensitive adhesive layer 122 is a softand adhesive material, which allows the first end portions 112 to beinserted thereinto when an external force is applied. The pressuresensitive adhesive layer 122 used in this exemplary embodiment is YM881(produced by Light Industry Institute, Fushun, China). The pressuresensitive adhesive layer 122 can, alternatively, be made of otheradhesive materials with high viscosity, such as glue. Moreover, thepolyester film 124 may be made of other polymers, such as polyethylene.

In another embodiment, the first protective layer 18 may only includethe polyester film 124. The polyester film 124 can be directly attachedto the carbon nanotube array 14 as follows: placing the polyester film124 on the carbon nanotube array 14; and pressing the first end portions112 of the carbon nanotube array 14 into the polyester film 124, therebyattaching the polyester film 124 to the carbon nanotube array 14.

In step 3, as shown in FIG. 7, the substrate 16 is removed from thesecond end portions 114, and the second protective layer 18′ is attachedto the second end portions 114. The second protective layer 18′ includesa pressure sensitive adhesive layer 122′ and a polyester film 124′. Thestep of attaching the second protective layer 18′ to the second endportions 114 is similar to that of the first protective layer 18 in thestep 3. Thereby, the carbon nanotube array 14 along with the twoprotective layers 18 and 18′ attached on the two opposite end portions112 and 114 thereof constitute an injection mold.

It is noted that step 3 is an optional step. The carbon nanotube array14 can form an injection mold along with the first protective layer 18attached to the first end portions 112 and the substrate 16 attached tothe second end portions 114. As a further alternative, the substrate 16could be permitted to remain instead of being replaced with the secondprotective layer 18′ and to thereby act as part of the injection mold.

In step 4, as shown in FIG. 8, the clearances 116 among the carbonnanotube array 14 are filled with the matrix material 12. This step canbe performed in the following manner: immersing the carbon nanotubearray 14 with two attached protective layers 18 and 18′ into a melt orsolution of the matrix material 12; taking the carbon nanotube array 14,now having the matrix material 12 filled among the clearances 116, outof the melted or solution of the matrix material 12; and curing thematrix material 12 among the clearances 116 in vacuum at roomtemperature for 24 hours, thereby causing the matrix material 12 tobecome soft and elastic. The matrix material 12 is advantageouslyselected from the group consisting of silica gel, polyethylene glycol,polyester, epoxy resin, and acrylic. In the preferred embodiment, thematrix material 12 is made from the Sylgard 160, a type of a 2-partsilicone elastomer, which is available from Dow Corning. The Sylgard 160is supplied, as two separate liquid components comprised of part A andpart B to be mixed in a 1:1 ratio by weight or volume. A mass percent ofthe CNTs in the carbon nanotube composite material is about 5 wt %.

In step 5, as shown in FIG. 2, both protective layers 18 and 18′ areremoved from the carbon nanotube array 14. The protective layers 18 and18′ can be removed, for example, by directly stripping off theprotective layers 18 and 18′ and sequentially dissolving away any of theremaining pressure sensitive adhesive layers 122 and 122′, by using anorganic solution. In the preferred embodiment, the organic solvent isxylene. Thus, the carbon nanotube composite material 10 is obtained,which has two end portions 12, 114 of the carbon nanotube array 14extending from the two surfaces 102 and 104 of the matrix material 12.

Preferably, the method for manufacturing the carbon nanotube compositematerial 10 can further include a reactive ion etching (RIE) step oranother selective material removal step to ensure the both end portions112 and 114 (i.e., both end portions of the respective CNTs) of thecarbon nanotube array 14 be sufficiently exposed. In the preferredembodiment, the RIE process is carried out using O2 plasma at a pressureof 6 pascals (Pa) and with a power of 150 watts (W) for 15 minutes (min)at each of the surfaces 102 and 104 of the matrix material 12. Finally,a carbon nanotube composite material 10 having the both end portions 112and 114 fully protruding out thereof is obtained.

The resulted carbon nanotube composite 10 can be further trimmed intoany desired geometrical figure for used as, e.g., electrical and/orthermal conductive component. In addition, since the CNTs of the carbonnanotube composite 10 are bounded tightly within the matrix material 12,a stability and reliability of the carbon nanotube composite 10 isimproved.

Referring to FIG. 9, electrical conductivities of the carbon nanotubecomposite material 10 are measured. The solid line represents axialconductivity along a direction parallel to longitudinal axes of theCNTs, and the dashed line represents lateral conductivity along adirection perpendicular to the longitudinal axes of the carbonnanotubes. As be expected to given the alignment of the CNTs, the axialconductivity, over the entire voltage range, is markedly higher than thelateral conductivity. As a result, when the carbon nanotube compositematerial 10 is aligned, the maximum performance of thermal and/orelectrical conduction and relative thereto along the axial direction canbe expected.

The two end portions 112, 114 of the CNTs of the carbon nanotube array14 are protruded out of two surfaces 102, 104. Thus, the two endportions 12, 114 of CNTs form thermal contact surfaces or electricalconnection surfaces directly in the axial direction, and the overallelectrical conductivity/thermal conductivity of the carbon nanotubecomposite material 10 is improved. The carbon nanotube compositematerial 10 can be formed in a desired pattern, according to theapplication requirement, and can, e.g., be in a film form that makesthem portable and integral. Moreover, the thickness and other dimensionsof the carbon nanotube composite material 10 can be chosen by thedesigner based on the use requirements and, thus, are not limited tothin film applications. For these reasons, the carbon nanotube compositematerial 10 can, e.g., be applied in a large-scaled IC and furthermorein any large-scaled electronic component. Additional uses for the carbonnanotube composite material 10 beyond the electronics area (e.g.,thermal transfer devices) are readily conceivable and are considered tobe within the scope of the present composite material.

Finally, it is to be understood that the embodiments mentioned above areintended to illustrate rather than limit the invention. Variations maybe made to the embodiments without departing from the spirit of theinvention as claimed. The above-described embodiments illustrate thescope of the invention but do not restrict the scope of the invention.

1. A carbon nanotube composite material comprising: a matrix materialhaving a first surface and an opposite second surface; and a pluralityof carbon nanotubes embedded in the matrix material, the carbonnanotubes being uniformly distributed therein in a desired pattern, eachof the carbon nanotubes having a first end portion and an oppositesecond end portion, the two opposite end portions of the carbonnanotubes respectively extending at least to the corresponding surfacesof the matrix material.
 2. The carbon nanotube composite material asclaimed in claim 1, wherein the two opposite end portions of the carbonnanotubes respectively extend out of the corresponding surfaces of thematrix material.
 3. The carbon nanotube composite material as claimed inclaim 1, wherein two opposite surfaces of the matrix material aresubstantially parallel to each other.
 4. The carbon nanotube compositematerial as claimed in claim 1, wherein each of the carbon nanotubes issubstantially parallel to one another.
 5. The carbon nanotube compositematerial as claimed in claim 1, wherein the carbon nanotubes aresubstantially perpendicular to the two opposite surfaces of the matrixmaterial.
 6. The carbon nanotube composite material as claimed in claim1, wherein the matrix material is comprised of a material selected fromthe group consisting of silica gel, polyethylene glycol, polyester,epoxy resin, and acrylic.
 7. A method for manufacturing a carbonnanotube composite material, comprising the steps of: providing asubstrate and forming a carbon nanotube array in a desired patternthereon, the carbon nanotube array defining a top end portion and abottom end portion, the bottom end portion being attached to thesubstrate, the carbon nanotube array having a plurality of clearancesamong neighboring carbon nanotubes of the carbon nanotube array;attaching a protective layer on the top end portion of the carbonnanotube array; filling clearances among the carbon nanotubes with amatrix material; and removing the first protective layer and thesubstrate from the carbon nanotube array so as to exposing the top endportion and the bottom end portion of the carbon nanotube array.
 8. Themethod as claimed in claim 7, further comprising the step of etching thematrix material adjacent the top end portion and the bottom end portionof the carbon nanotube array for further exposing the two end portions.9. The method as claimed in claim 7, wherein the first protective layercomprises a polyester film.
 10. The method as claimed in claim 9,wherein the first protective layer further comprises a pressuresensitive adhesive layer.
 11. The method as claimed in claim 7, whereinthe step of attaching the first protective layer comprises the steps of:placing the first protective layer on the top end portion of the carbonnanotube array; and pressing the first protective layer into the top endportion of the carbon nanotube array.
 12. The method for as claimed inclaim 7, wherein the clearances are further defined as being between thesubstrate and the first protective layer.
 13. The method as claimed inclaim 7, wherein matrix material is selected from the group comprisingof silica gel, polyethylene glycol, polyester, epoxy resin, and anacrylic.
 14. The method as claimed in claim 7, prior to the step offilling, further comprising the steps of: removing the substrate fromthe bottom end portion of the carbon nanotube array; and forming asecond protective layer on the bottom end portion of the carbon nanotubearray.
 15. The method as claimed in claim 14, wherein the secondprotective layer comprises a polyester film.
 16. The method as claimedin claim 15, wherein the second protective layer further comprises apressure sensitive adhesive layer.
 17. The method as claimed in claim 7,wherein the filling of clearances is achieved by an injection moldingprocess.